Apparatus for the coking of hydrocarbon oils



Aug. 15, 1 E. A-DESTREMPS APPARATUS FOR THE COKING OF HYDROCARBON OILS Filed May 21 1963 COKE TO REACTOR FIG-2 Edward A. Desrremps lnven'ror By, 9 @110 J Pcnenr Arforney United States Patent 3,336,114 APPARATUS FOR THE COKING OF HYDROCARBON OILS Edward A. Destremps, Murray Hill, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed May 21, 1963, Ser. No. 281,896 2 Claims. (Cl. 23-284) This invention relates to the thermal cracking of hydrocarbon oils and more particularly relatesto an improvement in the fluid coking of high boiling hydrocarbon oils such as residual petroleum oils, crude oils, pitches, etc.

Fluid coking of residual oils is a well-known process in commercial use wherein residual oil or other heavy petroleum oil is thermally cracked or coked in a coking reactor maintained at a cracking temperature. The oil is introduced into a fluid bed of solid inert particles such as coke and cracked to lower boiling hydrocarbons and coke which is deposited on the fluid solid particles.

To supply heat of cracking, coke particles are withdrawn from the coking reactor and passed to a burner where some of the coke particles are burned with air and their temperature is raised. The so-heated coke particles are then recycled to the coking reactor to supply the heat of cracking. More coke is produced during cracking than is necessary to supply the heat of cracking so that some of the coke product can be withdrawn as product. The coke withdrawn as product can be used for making electrodes for use in aluminum manufacture, as metallurgical coke and other uses. Where such coke has a high value it is uneconomica-l to burn the coke and it is preferred to supply heat by burning an extraneous fuel such as natural gas, methane or other hydrocarbon gases etc.

It has previously been proposed to reduce the amount of coke particles burned in a burner/ vessel by burning fuel oil or gas in an auxiliary burner attached to the coke burner vessel. To burn this fuel oil or gas, upwards of 50% excess air must be fired in the auxiliary burner to prevent the temperature of the burner vessel from going over 2800 F. which is approximately the maximum as limited by materials of construction. The excess air attacks the coke with a resultant loss of 510% of the product coke vs. 15-25% in normal operation of the fluid coking process. It is desirable to still further reduce the amount of product coke burned.

According to the present invention, substantially none of the product coke is burned when using an auxiliary burner with zero excess air. Instead of using air to quench the temperature in the auxiliary burner, a stream of coke from the burner vessel or reactor vessel is used. The flame temperature in the auxiliary burner can be controlled by controlling. the amount of coke particles recycled to the auxiliary burner from the burner vessel or reactor vessel.

In the drawing:

FIG. 1 represents a diagrammatic representation of a fluid coking unit; and

FIG. 2 represents an enlarged front elevation of the burner vessel showing the auxiliary burner means of the present invention with parts being shown in section to facilitate the disclosure.

Referring now to the drawing and FIG. 1, the reference character designates a line for feeding the oil to be cracked or coked to the coking reactor 12. The oil feed is any residual or heavy petroleum oil boiling above about 700 F. such as reduced crude oil, pitches, tars, etc. The coking reactor contains a fluid bed of solid particles, preferably coke particles made in the process and having a size between about 50 and 1000 microns. The reactor 12 is maintained at a temperature between about 850 F. and 1000 F. but where high temperature coking is de- 3,336,l l4 Patented Aug. 15, 1967 sired, temperatures up to about 2500 F. may be used. The pressure in the reactor may be between about 0 and 60 p.s.i.g. The fluidized bed in reactor 12 has a density between about 20 and 50 lbs./cu. ft. and the bed is maintained in a dense turbulent fluidized condition by passing gases and vapors upwardly through the reactor at a superficial velocity between about 0.1 and 5 ft./sec.

During coking the oil feed is converted to lower boiling hydrocarbons as vapors and carbonaceous residue which is deposited on the coke particles. The vapors and gases pass overhead through line 14 and are fractionated to separate naphtha and heating oil or gas oil from gases and products higher boiling than gas oil. Some coke particles are withdrawn from the reactor 12 through line 16, mixed with air from line 18 and passed to burner or heater vessel 22 which may be fluid bed burner or transfer line burner. A fluid bed 24 is shown in FIG. 2. The coke particles are maintained as a dense fluidized turbulent bed in the heater vessel by passing gas upwardly through the heater vessel at a superficial velocity between about 0.1 and 5 ft./sec. The density of the fluidized bed in burner vessel 12 is between about 20 and 50 lbs/cu. ft. The temperature in the heater vessel 22 is between about 900 F. and 1200 F. and the pressure is between about 0 and 60 p.s.i.g. The amount of coke particles circulating between the heater vessel 22 and reactor 12 is adjusted to keep the reactor at the desired temperature; the greater the rate of fresh oil feed to the reactor, the higher the heat load, and the greater the circulation rate between the reactor and the heater vessel.

More coke is made than is necessary to supply the heat of cracking or coking and excess coke as product may be withdrawn from line 16 through line 26 or from heater vessel through line 28 also shown in FIG. 2. Hot combustion gases pass overhead through line 32 and may go to a waste heat boiler or other heat exchanger to recover heat therefrom. The heated coke particles are continuously withdrawn from the burner or heater vessel 22 and recycled to reactor vessel 12 through line 34. Steam may be added to line 34 through line 36 if desired.

The fluid coking unit is disclosed in Pfeifl er et al. Patent 2,881,130 granted Apr. 7, 1959.

Referring now to FIG. 2, the heater vessel 22 is shown as a vertically arranged elongated cylindrical vessel pro vided with the dense fluidized bed 24 having a level indicated at 38 and a dilute phase 42 thereabove. A cyclone separator system 44 is shown including a series of cyclone separators each having a dipleg 46 for returning separated solids to the fluid bed 24. Solids outlet line 34 from heater vessel 22 has a control slide valve 48. Heater vessel 22 has a distribution grid 52 horizontally arranged in its lower portion above the inverted conical or tapered section 54 of burner vessel 22. Extending down from conical section 54 is a tubular vertical member 56 communicating with horizontally arranged passageway 58 which forms the outlet end of auxiliary burner 62. Tubular member 56 and passageway 58 are shown as being of substantially the same internal diameter.

The auxiliary burner 62 has an enlarged burning or ranged and of a larger diameter than outlet tube or passageway 58. At the other or inlet end of the burner 62 there is provided a pipe 66 which extends into the combustion chamber 64 a short distance and which introduces air and fuel gas to the chamber 64.

Air is introduced through line 68 and passed by pump 72 through line 74 provided with valve 76 and thence into line'66. Another line 78 having a valve 82 communicates with line 66 for introducing fuel gas such as methane, natural gas, or normally gaseous or liquid fuels, or the like, for admixture with the air being passed to the combustion chamber 64. If desired, line 78 may be concentric to line 66 so that fuelgas does not mix with air until it enters burner 64. The air in line 68 may be preheated in a furnace, if desired, to reduce the amount of air required. To control the amount of air introduced to combustion chamber 64, an air by-pass line 84 having a valve 86 is provided in line 74 between pump 72 and valve 76 for diverting air from line 74. A pilot lighter 92 is diagrammatically shown adjacent the outlet of line, 66.

According to the present invention the auxiliary burner 62 is provided to burn fuel gas or the like in preference to coke so that more coke is recovered from the process. However, if only fuel gas were burned in burner 62, the temperature would be too high for conventional structures. To prevent such high temperatures and to heat the coke particles at the same time, coke particles are recycled from the heater vessel 22 to the inlet end of burner 62 and combustion chamber 64 through line 96 which leads downwardly from the fluid bed 24 in burner or heater vessel 22. A valve 98 is provided in line 96 to control the rate of flow of solids through line 96 to burner 62.

The flame temperature in combustion chamber 64 can be controlled between about 1400 F. and 2800 F. by adjusting the coke circulation rate through line 96 by valve 98. No excess air is supplied by air line 68 so that combustion of the coke particles is substantially completely eliminated. The rate of circulation of coke through line 96 to combustion chamber 64 may be varied between about 5% and 100% of the amount of coke circulating between burner vessel 22 and reactor 12 to provide a flame temperature between about 1400 F. and 2800 F. in combustion chamber 64. The higher the flame temperature desired in combustion chamber 64, the lower the rate of circulation of coke through line 96 to combustion chamber 64. The density of the mixture in burner 62 may be between about 0.005 and 1.0 lb./ cu. ft.

Instead of using coke from heater vessel 22 to quench the flue gases in burner 62, coke from reactor vessel 12 and line 16 could be used. Since reactor vessel 12 is at a lower temperature than heater vessel 22, less coke would be needed to quench the gases in burner 62 if it were taken from reactor vessel 12.

The hot combustion gases and heated coke particles pass from the burner 62 through lines 58 and 56 into the bottom of burner vessel and through grid 52 to supply heat to the fluid bed of coke particles in the burner vessel 22.

For an 1800" F. temperature in combustion chamber 64, the coke circulation rate to combustion chamber 64 would be only about 28% of the amount of coke circulating between the coke burner or heater vessel 22 and the reactor 12, based on preheating the air to 1200 F. and using methane gas and no excess air.

Data were obtained in an experiment using a long horizontal furnace 15 feet long and 18 inches in internal diameter. The theoretical amount of air to support combustion was used and the temperature at the outlet of the auxiliary burner reached only 1800 F. versus about 3400 P. if no coke particles had been added. The data are as follows:

Air rate, s.c.f.m 350 CH, rate, s.c.f.m. 35 Coke rate, lbs/min. 4.0 Temperature at outlet of furnace 1800 F.

In a specific example a coking unit feeding about 6000 barrels per day of residual oil boiling above about 700 F. and having the following characteristics:

API gravity 0. Conradson carbon 30. Viscosity at 122 F. is 500 SSF.

The coke particles in the unit have a size between about 50 and 1000 microns. The temperature in the reactor 12 is about 950 F. and in the heater vessel 22 is about 1150 F. The hold up of coke particles in reactor 12 is about tons and in the heater vessel 22 about 45 tons. The density of the fluidized bed in reactor 12 is about 30 lbs/cu. ft. and in the heater vessel is about 30 lbs./cu.ft. The coke particles are circulated from the heater vessel 22 to the reactor 12 at a rate of about 7.5 tons per minute.

The combustion chamber '64 has a volume of about 275 cubic feet and is under a pressure of about 15 p.s.i.g. About 13,700 s.c.f.m. of air at a temperature of about 1200 F. are pumped through line 74 and admixed with about 1440 s.c.f.m. of methane at a temperature of about 77 F. Coke at a temperature of about 1150 F. from heater vessel 22 is passed through line 96 so that the temperature of the coke solids in the outlet end of chamber 64 and passing through lines 58 and 56 is about 1750" F. and the gas temperature 1800 F. Zero excess air is used so that substantially no coke particles are burned in auxiliary burner 62 or in heater vessel 22. For this temperature the amount of coke circulating through line 96 is about 28% of the amount of coke circulating between the heater vessel 22 and the reactor 12 if the air temperature in line 74 is preheated to about 1200 F., or 2.1 tons per minute.

The invention is not to be restricted to the specific embodiment or conditions given as these are by way of example only and are not intended to be restrictive.

What is claimed is:

1. An apparatus including a heater vessel, means for introducing finely divided solids into said heater vessel, means for withdrawing finely divided solids from said heater vessel, an auxiliary burner including an enlarged combustion chamber, means for introducing fuel and air into said combustion chamber at the inlet end thereof for combustion therein, the outlet end of said auxiliary burner communicating with the bottom portion of said heater vessel, a line connecting said heater vessel and said combustion chamber adjacent said inlet end and said means for introducing fuel into said combustion chamber whereby solids may be recycled from said heater vessel to the inlet end of said combustion chamber to modify the temperature of the burning fuel in said combustion chamber.

2. An apparatus including in combination a heater vessel, a reactor vessel, means for introducing finely divided solids into said vessels, means for withdrawing finely divided solids from said vessels, an auxiliary burner including an enlarged combustion chamber, means for introducing fuel and air into said combustion chamber at the inlet end thereof, the outlet end of said auxiliary burner communicating with the bottom portion of said heater vessel, a line communicating with said reactor vessel and the inlet end of said combustion chamber whereby solids may be withdrawn from said reactor vessel and introduced into said inlet end of said combustion chamber to modify the temperature of the burning fuel therein.

References Cited UNITED STATES PATENTS l/l955 Brown 208 4/ 1959 Pfeifier et al. 208127 

1. AN APPARTUS INCLUDING A HEATER VESSEL, MEANS FOR INTRODUCING FINELY DIVIDED SOLIDS INTO SAID HEATER VESSEL, MEANS FOR WITHDRAWING FINELY DIVIDED SOLIDS FROM SAID HEATER VESSEL, AND AUXILIARY BURNER INCLUDING AN ENLARGED COMBUSTION CHAMBER, MEANS FOR INTRODUCING FUEL AND AIR INTO SAID COMBUSION CHAMBER AT THE INLET END THEREOF FOR COMBUSTION THEREIN, THE OUTLET END OF SAID AUXILIARY BURNER COMMUNICATING WITH THE BOTTOM PORTION OF SAID HEATER VESSEL, A LINE CONNECTING SAID HEATER VESSEL AND SAID COMBUSTION CHAMBER ADJACENT SAID INLET END AND SAID MEANS FOR INTRODUCTION FUEL INTO SAID COMBUSTION CHAMBER WHEREBY SOLIDS MAY BE RECYCLED FROM SAID HEATER VESSEL TO THE INLET END OF SAID COMBUSTION CHAMBER TO MODIFY THE TEMPERATURE OF THE BURNING FUEL IN SIAD COMBUSITION CHAMBER. 